Chapter 5 - Intraoperative neurophysiological monitoring during brainstem surgery

Brainstem surgery is challenging due to the high concentration of essential neural structures such as cranial nerve nuclei, sensorimotor and auditory pathways, as well as the reticular formation. Therefore, even a small injury to the brainstem can hinder the functional integrity of one or more of these neural pathways and result in neurological deficits. Intraoperative neurophysiology aims not merely to predict but also to prevent neurological injury, thanks to the tailored intraoperative use of standard clinical neurophysiological techniques such as electromyography, and somatosensory, brainstem auditory and motor evoked potentials. Monitoring these potentials allows to prevent an injury to the long pathways within the brainstem. In addition, mapping techniques provide functional identification of critical anatomical landmarks, whenever their visual identification is ambiguous, to select the safest entry route to the brainstem. In this chapter we critically review the various intyraoperative mapping and monitoring techniques that can be used during surgery for lesions in the midbrain, pons, and medulla oblongata.